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Exhaust fumes smell bad. In fact, terrible!
But being Carbon Monoxide-rich, it can even suffocate you to death.
Therefore, let’s agree on the point that the exhaust smell you’re smelling around your house right now, is a serious threat. And you have to leave no stone unturned to find its source and fix it up, once and for all.
But how’ll you start the search? Is it just a tiny leak in the flue, or a clogged up inlet vent? Or something more complicated?
Worry not. On your behalf, we’ve gone through the hectic process of research to find 4 actionable solutions for you. This article will take you through every possible source of the exhaust fume invasion, and provide you with an actionable solution to each.
Put your handyman helmet on, and let’s start-
Step Zero: Beware of Carbon Monoxide(CO) Suffocation
Before taking care of the exhaust leak(or so), let’s secure our health first.
No matter if you’ve figured out the source of the exhaust smell or not, take measures to calculate the level of CO in the first place. CO comes hand to hand with any exhaust fumes and it can suffocate your breath to death.
Whenever you’ve figured out the exhaust smell around, shut off all the appliances that burn gas or oil(furnace, water heater, etc). Get yourself a Carbon Monoxide Detector(CO monitor) and place it near the possible source of the smell.
Kidde has got a convenient CO monitor that shows CO level in PPM(parts per million). According to that chart, anything above 100 PPM is dangerous for both adults and kids.
Now, there is a certain detection time that it takes. For example, it will display an alarm of 150PPM after 10-50 minutes of continuous exposure at a Co level of 150PPM. Here’s the full safe carbon monoxide levels chart and scheduling.
What Causes Exhaust Smell in House? 4 Causes & Fixes
You’ve maybe asked a hundred times that- “Why do I smell exhaust fumes in my house?” for the last few days. Guess what, we’ve got 4 possible answers to that, with a solution to each of them.
Take time to go through them in-depth and identify which one has taken place in your home-
1 of 4: A Faulty Flue Ducting
As long as we’re smelling an exhaust smell around, maybe the exhaust air can’t escape properly and backfiring to the home. And the frontline reason for that can be a Faulty Exhaust ducting.
Makes sense, right?
So, what are we addressing as faults of an exhaust duct that might cause exhaust smoke invasion? According to Angie’s List forum user LCD, they are-
- Rusted through the flue ducting.
- Ducting parts got separated/leaks.
Here’s an identifier that helps you understand if your flue has these three issues or not-
You might have cleaned up the whole ducting right after the exhaust smell had been smelt for the first time. But guess what, the smell became even more after the cleanup.
And that can happen only if the flue has got one of these issues. A clean-up had even enlarged the damage and drew more exhaust fumes in!
Although we’re addressing a faulty flue/exhaust ducting, the three defects have their unique ways of fixing. We’ll talk in-depth about those fixes of chimney flue.
But before that, let’s figure what happened to the ducting exactly.
Step 1: Pinpoint the reason
No matter if it’s a rust invasion or separated ducting parts, you need to be certain about it first. Once again, thanks to Angie’s List user LCD for suggesting this method.
You’d need this equipment-
Now, shut off the entire system and take off the roof cap. Enlighten the ducting from the bottom using the flashlight, and keep inserting a drop light from the top of the ducting.
Making sure that you can clearly see into the duct, check deeply for the broken/damaged/rusty part of the duct that we’ve talked about.
Once you’ve got an eye on the damage, proceed to the next step.
Step 2: Get off The Rust
Let’s say, you’ve found a rusted flue pipe or portion of the flue that had caused a partial gap/damage within the duct body. How’d you fix that rust in furnace flue? Or maybe go for a new replacement flue maybe?
Well, as long as it’s not-so-spread rust catch, it’s fixable. Take a look at this 3-step process-
- Use a wire brush to eliminate the loosen up rusty stuff.
- Use mineral spirit to de-grease the affected part. By that, the oily stain caused by the exhaust fumes will go away.
- Now it’s the stubborn part of the rusty flue pipe. Give a few coats of zinc-rich cold galvanizing spray paint on the entire rust.
- Dry it to touch and place the flue back. Usually, it takes up to 30 minutes to dry.
Done this way, there will be no further rust spread-out anytime soon.
Step 3: Fix the Broken Flue Pipe Parts
Sometimes, because of aggressive rust invasion, the flue can be broken or separated between parts. This might be even more likely of a cause why the exhaust fumes are U-turning on their way through the ducting.
Once the rust is taken care of (step 2), seal the broken parts/leaks of it. You can patch up the leaks with small, moldable sealants if they’re small. If they’re large in size, you might need an entire insulation around the damaged area. Wrapping the entire area with a roof tape might be good flue duct insulation.
However, if you find the flue beyond repair, you can replace it with a new one. Here’s a step by step guide on furnace flue pipe replacement.
2 of 4: Partially Blocked Airflow
An interruption to the entire HVAC airflow can turn the system down. And it all starts from reverse-directing the exhaust fumes into the house.
So what kind of airflow blockage we’re talking over here? Well, not the one that’s caused by a broken, leaky and rusty flue ducting(as we’ve covered this earlier). We’re rather focusing on external factors that block airflow from vent.
Some of such scenarios can be-
- Something like a bird’s nest or insects got into the duct cap/furnace cap on the roof. If any such things hang on their(maybe on a screw or so), it might direct the upward exhaust air back into the flue.
- A blockage of the fresh air inlet of your newly installed HVAC devices(water heater, heater, ac, furnace, etc) by dust, birds, bird nest or insects. This will induce weak combustion and blowout partially burned gas through the system.
The simple fix is to get rid of whatever blockage your vents or furnace crown has got blocked with. It can be a bird’s nest, a bird(alive or deal), dust, debris, and other macro-contaminants.
Blockage Type 1: Bird/ Bird Nest in Air Duct
If it’s a bird’s nest or alive bird, beware of reaching any kind of harm to them physically while you’re leading them out. If it’s nested in the chimney, there’s not much to do instead of relocating it nearby.
In fact, in the UK it’s legally restricted to shift bird’s nest without their knowledge.
Blockage Type 2: Dust and Debris
On the other hand, dust and dusty particles can also block the inlet or exhaust up. This happens more with high-efficiency furnace that’d been kept uncleaned for years. While your home is built new, there also can be construction debris in air ducts.
The good news is, getting rid of a dusted inlet is easy. All you need to do is follow these steps-
- Step 1: Locate the exit point of your intake/exhaust pipes.
- Step 2: Open up the vent pipe with a screwdriver.
- Step 3: Extract the large-in-size dirt and debris out of it.
- Step 4: Use a brush or soft cloth to remove sticky dirt and debris.
- Step 5: Finally, use air duct cleaning vacuum to clean the entire vent thoroughly.
- Step 6: Check for any further blockage with a wire hanger shaped into a shepherd’s crook.
- Step 7: Close the pipe up with the screwdriver.
3 of 4: Uninvited Garage Fumes in House
A ‘Health Canada’ study had found that- houses with attached garage can contain a significant amount of benzene(a gasoline related pollutant). Even states like Colorado, Minnesota, Alaska, and Lowa had also found houses with such garage-generated CO leaks.
It’s quite hard to stop fumes from finding their ways into your home through gaps, leaks, and cracks. Hence, we’ve got a checklist that might give you a 99% certainty in this regard-
Seal Garage Cracks on The Ceiling
Do a thorough assessment to find every kind of gaps/holes/leaks/cracks from your garage to the home. This list might include a non-air-tight door between the garage and home.
If you’ve found any, use supplies like spray foam, putty, caulk, and weatherstripping, etc. Use these supplies to seal any penetration caused by ducting, wiring, etc.
Finish The Drywall and Ceiling Well
For newly made homes, it’s often for the ceiling and the drywall to have unfinished joints. As you know, those tiny cracks are enough for the exhaust fumes to find a way into the home.
To fix this up, check the drywall and it joints in-depth if they’re properly sealed with tape and compound. The primer and paint have to be checked for any leaks as well.
Burn Oil or Gas with Care
Exhaust fumes are generated from oil or gas burner, which you have to do every now and then in your garage. For reasons, this might intrude and cause oil burner exhaust smell in house. Same goes for gas exhaust smell in house as well.
For safe play, we’d suggest you run those power tools/engines as close to the doors/windows as possible. Use a separate exhaust vent for that.
4 of 4: It’s Coming from The Neighbourhood
Although it’s a weak possibility, we would like to check for a closely placed exhaust vent through the wall near the ground level. If the furnace/heater system of your neighbor is large enough, it might get through your air inlets and cause the exhaust smell.
The closer you live to such neighbors, the more likely this is to happen.
Simply put, either you or your neighbor need to set the two vents(your neighbor’s exhaust and your inlet) at a distance. A simple request on that might work most of the time.
Asking them to add a ducting on top of the exhaust and direct it towards the rooftop might be a good idea, as moving your inlet vents is a way more complicated job.
4 Tips to Stop The Exhaust Gas Coming Back Again
Don’t want to host the exhaust like smell in the house over again? Here’s some tips in this regard-
Keep Your Ventilation System Clean
Residential air vents are full of duct, dirt, hair, spider web, etc. Cleaning them up on a regular basis(once in a month) will boost the HVAC system, save your money and prevent unwanted exhaust fumes from getting into the house.
Use tools like a heavy-duty vacuum cleaner, cleaning brush, wire brush, broom, etc as a cleaning tool. Make sure the vacuum has a long hose to reach deep into the vents. This will bring out the molds and mildew buildups inside the air ducts.
Also, clean the grills in your ceiling on a regular basis.
Don’t Keep the Inlet and Exhaust Close
We’ve not seen many people to do so, but it’s quite stupid to keep your air inlet and exhaust outlets close to each other. Although inlet pipes face downwards and the exhaust faces upward, but being close to each other, the inlet can such up the exhaust gases back into the home.
Therefore, keep them at a distance of at least 5 feet. Keep the areas nearby clutter-free(plants, debris, etc).
Bird-proof the Furnace Vent Cap/Chimney Cap
Apart from rainproofing the crow/cap of your roof vent, it’s quite important to protect it not to let the birds/insects get in. You can start by installing a wire mesh into it. And seal it well from the ground insects.
The best solution would be anyway, to get a ready-made furnace cap that checks all of the security features. Otherwise it won’t be surprising to figure out dead animal in air duct once in a while.
Here are some recommendations-
- Best round-shaped(8”-18”) chimney cap: Draft King SS10U
- Best rectangular chimney cap: Shelter SCADJ-S
- Best wind-directional flue cap: Famco WDC6
- Best size(mesh+dimension) diversity: HY-C SC99
- Best No-mesh flue cap: SMOKEWARE Vented Chimney Cap
Keep Your Air Filter in Good Health
Apart from cleaning the furnace filter on a regular basis, you’re also advised to keep it on check for misplacement or break. Often, due to overuse or unfit filter slots, air filters get displaced or bent. Done so, it will definitely not be able to keep the exhaust fumes and smell away as it’s supposed to be.
So, check for a misfit or damage or clogged-up situation of the furnace filter on a regular basis.
Making sure that you’ve gone through everything we’ve written, we’re sure that you know the sources of the smell of exhaust fumes in house and how to fix them.
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.